PITTSBURG — A Concord nanny accused of molesting two young girls under his care sat in court Tuesday listening to testimony from an officer who observed the police interview of one of the alleged victims in the case.

Joaquin Sierra-Cruz, 51, whose name is also listed as “Joaquin Sierra” and “Joaquin Cruz” in court documents, sat solemnly during a preliminary hearing in a Pittsburg courtroom, occasionally shifting in his seat, as he listened to Orinda police Sgt. Michael Berry testify that Sierra-Cruz’s second alleged victim — who was younger than 11 when the alleged molestation occurred — described to authorities how Sierra-Cruz would touch her breasts, and sometimes touch his own private parts, as he drove her home to Orinda from her school in Alameda County.

Sierra-Cruz’s defense attorney, Joseph O’Sullivan, aggressively cross-examined the sergeant, arguing that many of the questions posed to the alleged victim during the interview were asked improperly. He also highlighted contradictions in the statement by the alleged victim, who at one point said Sierra-Cruz had molested her in a particular van as far back as October 2014 and at another point said the defendant had only been driving the van since about January 2015.

In May, Sierra-Cruz was charged with 10 child molestation counts, all felonies, including sexual penetration with a minor and oral copulation with a minor. Antioch police said at that time that Sierra-Cruz was a certified nanny who helped his wife in her child care business, and that two girls under his care had reported to authorities that he’d sexually molested them.

Six of the alleged offenses happened during the summer of 2008, and the other four happened from October 2014 to January 2015, according to the complaint against him. The two alleged victims — one of them younger than 7 years old at the time, and the other 11 — reportedly knew one another and were friends, police said.

Berry. who watched the interview with the second alleged victim (“Jane Doe 2” in court documents) testified that the girl told authorities Sierra-Cruz had touched her breast one day on the way home from school in October 2014, and that he continued to touch her regularly after that. The girl told authorities the molestation happened in the car, often when traffic would come to a stop, and that on four occasions he pulled out his penis and began masturbating, Berry testified.

Berry also testified that the girl had said Sierra-Cruz told her not to tell anyone, and bought her several containers of a skin care product she liked in return for allowing him to touch her. O’Sullivan brought that up during cross-examination.

“Did she allow the touching?” O’Sullivan asked, pointing out that Berry had just testified the alleged victim had also told authorities she asked Sierra-Cruz to stop the first time he touched her.

“I believe on the occasion he gave (the skin care product) to her, she did,” Berry replied.

Earlier in the day, before Berry took the stand, O’Sullivan argued that the questions posed to Jane Doe 2 were “so convoluted that it makes the answers useless.” He also argued that because Berry didn’t actually interview the girl, the defense was at a “distinct disadvantage” during cross-examination.

Judge Charles Treat allowed the testimony to proceed.

An officer who interviewed the first alleged victim is expected to testify on Jan. 12, when the hearing is scheduled to resume.